Böckmann Rainer A, Hac Agnieszka, Heimburg Thomas, Grubmüller Helmut
Theoretical Molecular Biophysics Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
Biophys J. 2003 Sep;85(3):1647-55. doi: 10.1016/S0006-3495(03)74594-9.
Electrostatic interactions govern structural and dynamical properties of membranes and can vary considerably with the composition of the aqueous buffer. We studied the influence of sodium chloride on a pure POPC lipid bilayer by fluorescence correlation spectroscopy experiments and molecular dynamics simulations. Increasing sodium chloride concentration was found to decrease the self-diffusion of POPC lipids within the bilayer. Self-diffusion coefficients calculated from the 100 ns simulations agree with those measured on a millisecond timescale, suggesting that most of the relaxation processes relevant for lipid diffusion are faster than the simulation timescale. As the dominant effect, the molecular dynamics simulations revealed a tight binding of sodium ions to the carbonyl oxygens of on average three lipids leading to larger complexes with reduced mobility. Additionally, the bilayer thickens by approximately 2 A, which increases the order parameter of the fatty acyl chains. Sodium binding alters the electrostatic potential, which is largely compensated by a changed polarization of the aqueous medium and a lipid dipole reorientation.
静电相互作用决定了膜的结构和动力学性质，并且会随水性缓冲液的组成而有很大变化。我们通过荧光相关光谱实验和分子动力学模拟研究了氯化钠对纯POPC脂质双层的影响。发现增加氯化钠浓度会降低双层内POPC脂质的自扩散。从100纳秒模拟计算出的自扩散系数与在毫秒时间尺度上测量的结果一致，这表明与脂质扩散相关的大多数弛豫过程比模拟时间尺度更快。作为主要效应，分子动力学模拟揭示了钠离子与平均三个脂质的羰基氧紧密结合，导致形成流动性降低的更大复合物。此外，双层厚度增加约2埃，这增加了脂肪酰链的序参数。钠结合改变了静电势，这在很大程度上由水性介质极化的变化和脂质偶极子重新定向所补偿。
